Antenna circuit modulation



Nov. 9, 1937.

ANTENNA CIRCUIT MODULATION Filed July l5, 1936 G. H. BROWN 3 SheetSr-Sheet 1 Gttorneg Nov. .9, 1937.

G. H. BROWN ANTENNA CIRCUIT MDULATION Filed ,July 16, 1936 3 Sheets-Sheet 2 nv-entor 6605.7@ f'own/ Nov. 9, 1937. 4G. H. BR'owN ANTENNA CIRCUIT MODULATION Filed July 16, 1956 .3 Sheets-Sheet 3 Snventon: 66073615., rwm

Gtforneg Patented Nov. 9, 1.937A

muren srarss ANTENNA CIRCUKT MODULATION George H. Brown, Haddoniield, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application .l'uly 16, 1936, Serial No. 90,825

11 Claims.

My invention relates to modulation systems. More specifically my invention is a radio system in which the modulation of carrier currents' isA effected by radiating a carrier wave from one antenna and sideband waves from two or more antennas spaced from the carrier current antenna.

In a conventional modulation system, carrier currents and modulation currents are impressed on an amplifier or modulator stage or stages. If

the modulation is complete, i. e. one hundred percent, the amplifier or modulator stage must be able to handle four times the carrier power.

The provision for the peak modulation requires an amplifier power capacity which is far in excess of average requirements. This means low average operating efliciency. A power amplifier, of this type, is not only inefficient but relatively costly.

I propose to provide a modulation system in' which the carrier currents are impressed on one antenna. The carrier currents will be amplified without being modulated. Since the carrier current amplier may be operated continuously at its rated capacity, its efficiency will be high. The side bands, without carrier, may be fed to a plurality of separate antennas. The y'waves from the carrier antenna and the waves from sideband antennas will be propagated substantially asa conventional antenna system propagates a modulated carrier wave.

One of the objects of my invention is to provide a novel means of establishing a modulated Wave in space. f n

Another object is to provide means for radiatingv an unmodulated carrier wave from one antenna and simultaneously radiating modulation waves from separated antennas to effect modulated carrier Waves at points remote .from the antennas.

`Another object is to provide Va plurality of means for radiating waves comprising: An unmodulated carrier, an upper side band, and a lower side band.

A still further object is to provide a'system with means for radiating an unmodulated carrier wave Vfrom one antenna, and modulating said carrier at a remote receiver by radiating the modulation waves from a plurality of antennas spaced from they carrier antenna.

,50 My invention may be best understood by refer- V55 modification of my invention,

(Cl. Z-17) Fig. 3 is a graph showing the characteristic modulated field pattern of the system of Fig. 2,

Fig. 4 is a schematic diagram of a modcation of the system of Fig. 2,

Fig. 5 is a graph showing the characteristic 5 modulated field pattern of the system of Fig. 4, and,

Fig. 6 is a schematic diagram of the system of Fig. 1 applied to a short wave Vertical antenna system. 10

In Fig. l a crystal oscillator I generates a current of frequency F. Currents of frequency F are fed through a buffer stage 3 to a balanced modulator 5. The modulating'currents of frequency fv are impressed through a microphone l 15 or the like, on a speech amplifier 9. The amplied modulating currents of frequency v are impressed on the balanced modulator 5. The output of the balanced modulator supplies currents of frequency'F-I-fv'v and F-fv. The currents of 20 these frequencies (F-l-fvv and F-fvv) are separated by filters Il, I3.

The carrier frequency currents fc, generated by thecarrier crystal oscillator I5, are impressed through a carrier wave amplifier I6 and a trans- 25 former I'I or other coupling means, in an antenna I8 which radiates the unmodulated carrier wave of frequency fc. Currents of frequency F and fc, respectively, supplied by the crystal oscillator I and carrier crystal I5 are impressed on a modu- 30 lator I9. This modulator establishes currents of frequency fc-l-F and fc-F. A suitable filter 2| attenuates the former frequency fc-l-F and passes currents of the latter frequency ,fc-F. The last mentioned currents ,fc-F and currents of frequency F-fv are impressed on a modulator 23. YThe output of this modulator includes currents offrequency fc-fv and other components which may be neglected. The currents of frequency fc-fv are one of the sidebands resulting 40 from the difference between carrier frequency fc and the modulation frequency iv. These currents are fed through a transformer 25 to the antenna 2l from which waves of frequency fc-v are radiated. 45

Currents of lfrequencies fc-F and F-I-v are Vimpressed on a modulator 29. The output of modulator 29 includes currents of frequency fc-i-fv are radiated. Thus it will be seen that the foregoingrarrangement establishes currents of three 50 frequencies:V carrier fe, upper side band fc-l-fv and lower side bandje-jv.

lf the antennas I8, 2l and 33 are widely spaced,

CAD

so that there is no radiation coupling, it can be shown that a .space modulated wave will be If the radiators cannot be placed a wave length Y or more apart, the reactive component of the radiation coupling can be nulliiied by using a link circuit to induce voltages in phase opposition to the reactive couplingvoltages. The mutual resistance term can be made Zero by spacing they antennas .45, .9, 1.5, 2.0, or 2.5 etc. wave lengths apart. Assuming that both couplings are zero, the carrier power represents 100 units, the average power supplied by the transmitter for 100% modulation 150 units, and the peak power for 100% modulation 150 units. In contrast a conventional modulation system has carrier power 100 units, average power 150 units, and peak power of 400 units. This indicates avery substantial saving in power, apparatus and maintenance, and a corresponding increase in efficiency in favor of the space modulated system. The foregoing improvement is due in part to the very high efciency of the carrier wave amplifiers. The side band modulators or amplifiers operate at high efficiency on peak modulation, the amount of power being transmitted through the modulator-amplifiers is so small in comparison to the carrier power that the 10W eiciency is not important.v

Although the foregoing system represents a preferred form of my invention and Yproduces a space modulated wave which has a uniform circular eld, a moreV simple method Vmay be employed at the expense of a less perfect space modulation field. -In Fig. 2 a system` is shown in which currents representing side band frequencies fc-l-fv and fc-fv from source 35 are impressed in phase opposition on the antennas 31, 39. Currents of carrier frequency are impressed from a suitable source il on the center or carrier frequency antenna 43.

In the system of Fig. 2 the carrier frequency currents fc are-separate from the curents of side band frequencies ifv.' `The antenna arrangement is adjusted so that the equal and oppositely phased currents in the sideband antennas induce no voltages in the center or carrier current antenna. Likewise the center antenna induces no carrier currents in the side band antenna circuits.

The system of Fig. 2 propagates waves of carrier frequency throughout a uniform circular field. The side band radiation follows a figure 8 pattern. While these fields produce a space modulated wave which may be received throughout most of the service area, the percentage modulation varies with respect to the angle between a line joining the antennas, and the line from the center antenna to the receiver.

If the antennas are spaced one quarter Yof a wave length and e is the angle between the line through thetransmitting antennas and the line from the center antenna to the receiver, the modulation factor will be a maximum when 9=0 and zero when 9:90?. The modulation factor has been plotted against the angle int degrees in the graph X shown in Fig. 3. In thesystem of Fig. 2 the carrier power may be represented as 100 units, the average power supplied for 100% modulation 111.2 units, and the peak power supplied for 100% modulation 141.8 units. These figures indicate a substantial improvement in efficiency over the conventional modulation system.

The system illustrated in Fig. 2 has a disadvantage in the variation of the percentage of modulation with the angle 9. This disadvantage may be minimized by employing a plurality of radiators of currents cf side band frequency as shown in Fig. 4. In the arrangement of this antenna array, the unmcdulated carrier currents from source 45 are impressed on the antenna 4i'. The upper and lower side band current fai-fv are mpressed on the sideband antennas 49, l, 53, 55, 51, 59. The distance d between the several antennas is .45 of a wave length. The modulation factor is now represented in terms of the angle G in the graph Y shown in Fig. 5. The relative power of the carrier, average power, and peak modulation are, respectively, 100, 128.6 and 1.41.8 units.

If the waves to be propagated are of short length, it becomes practical to dispose a plurality of dipoles along a vertical line as sho-wn in Fig. 6. In this array the antennas are preferably half wave dipoles spaced about one half wave apart. The center antenna 5i is fed by a transmission line E3 from a carrier current source S5. The upperside band may be supplied by the circuit arrangement of Fig. 1 and impressed on the upper dipole 6l through a transmission line 59 from a source 'I I. The lower side band may be similarly supplied and impressed on the lower dipole 'i3 through a transmission line 'i5 from a source Tl.

In the arrangement of Fig. 6 the power requirements are the same as the system of Fig. 2. The carrier and sidebands establish circular fields about the vertical line through the antennas. 'Ihe modulation factor will be the same at all points within the service area including points above and below the horizontal plane through the center of the carrier Wave.

Instead of supplying the upper sideband to the upper antenna and the lower sideband to the lower antenna, the sidebands may be supplied to both upper and lower antennas in accordance with the system of Fig. 2. In this case for 100 units of carrier power, the average power for 100% modulation is 125 units, and the peak power is 150 units. The modulation factor will be uniformly 100% throughout a service area in a horizontal plane throughthe center of the center antenna but will decrease for planes above and below such service area.

Thus I have described an antenna circuit modulation system in which unmodulated carrier frequency currents are impressed on an antenna and radiated therefrom in a field of circular pattern. Modulation currents are impressed as upper and lower sidebands on Vother antennas suitably positioned with respect to the carrier frequency radiator. The sideband currents may be radiated as elds of circular, figure 8, or other patterns. A receiver within the service area combines the several currents which are amplified and demodulated in the conventional manner. Substantial savings in power, and increased efficiency may be obtained by application of the foregoing systems. It should be understood that the actual Yappara.- tus and antenna arrays of my invention may follow numerous arrangements which will be obvious, in view of the foregoing description, to those skilled in the art.

I claim as my invention:

1. An antenna modulation system comprising a plurality of antennas, means for impressing an unmodulated carrier current on one antenna, means for impressing an upper side band current on a second antenna, means for impressing a lower side band current on a third antenna, and means for minimizing radiation coupling between said antennas.

2. An antenna modulation system comprising a plurality of antennas spaced at least .45 of a wave length from each other, means for impressing an unmodulated carrier current on one of said antennas, means for impressing an upper sideband current on another of said antennas, and means for impressing a lower sideband current on a third of said antennas.

3. A transmission system including in combination a plurality of antennas, means for impressing in phase opposition upper and lower` side band currents on a pair of said antennas, and means for impressing unmodulated carrier currents on a third antenna of said plurality, said plurality of antennas being so constructed and arranged that substantially no carrier currents are induced in said pair of antennas, and substantially no sideband currents are induced in said third antenna.

4. A transmission system including in combination a plurality of antennas, means for impressing in phase opposition upper and lower side band currents on pairs of said antennas, and means for impressing unmodulated carrier currents on a third antenna of said plurality, said plurality of antennas being so constructed and arranged that substantially no carrier currents are induced in said pairs of antennas, and substantially no sideband currents are induced in said third antenna.

5. An antenna modulation system comprising in combination a plurality of dipole antennas disposed substantially along a common line and spaced apart, means for impressing sideband frequency currents on two of said antennas, and means for impressing unmodulated carrier frequency currents on one of said antennas positioned between said two antennas.

6. An antenna modulation system comprising in combination three half wave dipole antennas spaced a half wave length apart and disposed along a common vertical line, means for impressing unmodulated carrier frequency currents on the centrally disposed one of said antennas, means for impressing currents of one sideband frequency on the upper of said antennas, and means for impressing currents of the other of said sideband frequency on the lower of said antennas.

7. An antenna modulation system comprising in combination three half wave dipole antennas spaced a half Wave length apart and disposed along a common Vertical line, means for impressing unmodulated carrier frequency currents on the centrally disposed one of said antennas, and means for impressing currents of upper and lower sideband frequency in phase opposition on the upper and lower of said antennas.

8. The method of transmitting intelligence which comprises radiating from an antenna an unmodulated carrier wave, radiating from a pair of antennas wavesof upper and lower sideband frequency in phase opposition, and combining said waves at a point remote from the origin of said radiation.

9. 'Ihe method of transmitting intelligence which comprises radiating from a centrally disposed antenna an unmodulated carrier wave, radiating from antennas on opposite sides of said centrally disposed antenna waves of upper and lower sideband frequency in phase opposition, preventing the interaction of said waves at their sources, and combining said waves at a point remote from the origin of said radiation.

10. The method of transmitting intelligence which comprises radiating from a centrally disposed radiator an unmodulated carrier wave, radiating from a plurality of sources -disposed on opposite sides of said centrally disposed radiator waves of upper and lower sideband frequency in phase opposition, and combining said waves at a point remote from the origin of said radiation.

11. The method of transmitting intelligence which comprises radiating an unmodulated carrier wave, radiating from'a plurality of sources waves of upper and lower` sideband frequency in phase opposition, preventingthe interaction of said waves at their point of radiation, and combining said waves at a point remote from the origin of said radiation.

GEORGE I-I. BROWN. 

